Radial Force Measurements Research Articles

Do Balloon Catheters have a Different Radial Force Along Their Longitudinal Axis?

PurposeThis experimental study was designed to compare radial forces between the central portion and both ends of balloon catheters when dilating stenosis.Materials and MethodsThree balloon catheters of 6 and 8 mm in diameter and of variable length were tested: Mustang, Conquest, and Genoss PTA. Cylindrical modules to position balloon catheters and install the measuring tip during radial force measurements were made using a 3D printer. The measuring tip created 20% stenosis at the inner lumen. Both ends and center of the balloon catheter were located at the measuring tip. The radial force was measured after inflating the balloon catheter to the rated burst pressure.ResultsFor the different diameters and lengths of balloon catheters and cylinder sizes, the median inccenter, the radial rease in radial force at the distal end compared to the center was 16.5% (range: 9.8–35.2%) for Mustang, 12.4% (range: 10.3–25.5%) for Genoss, and 7.4% (range: −0.3–13.1%) for Conquest balloon catheters. Similarly, compared to that at the force at the proximal end was 10.8% greater (range: −2.9–18.3%) for Mustang, 9.9% greater (range: 3.9–22.3%) for Genoss, and 7.3% greater (range: −1.3–12.4%) for Conquest catheters.ConclusionThe radial force is greater at both ends of the balloon than at the central portion, especially at the distal end. Dilation using the distal end of the balloon catheter is a practical method that can be applied in clinical practice without additional devices when encountering resistant stenosis, especially with semi-compliant balloons.Graphical

Quantitative radial force measurements of Woven EndoBridge devices.

Lateral/radial forces and the mechanical properties of Woven EndoBridge (WEB) devices have significant importance for therapeutic success. In other words, adequate apposition of the lateral wall of a cerebral aneurysm is critical for preventing recurrence or re-rupture risk. This study aimed to investigate the pressure values applied by different WEB devices to the lateral walls of aneurysms and the relationships between these pressure measurements and the diameters of WEB devices. By placing four WEB devices of different sizes and types between two rigid metal plates, the lateral forces applied by these WEB devices to plates of different apertures were measured quantitatively. We tested a single device of each size over multiple periods. The total number of examined WEB devices is four. There was a significant negative relationship between plate distances and pressure values (correlation coefficient:-0.956, p = 0.000). The lateral wall apposition pressure of a 4- or 5-mm aperture size was higher than a 6-mm aperture size for SL-type WEB devices with a 7-mm diameter. Similarly, the lateral wall apposition pressure detected for a 3- or 3.5-mm aperture size was higher than a 4-mm aperture size for W5-4.5-3 and W5-5-3.6. It was observed that maximum lateral wall pressure was detected in plate measurements of SLS-type devices compared to SL-type devices. The diameter and height values of 3 of the 4 unconstrained WEB devices analyzed differed from the catalog values. It seems that SLS-type devices apply more pressure on the aneurysm's lateral borders than SL-type devices.

Comparison of aortic valve repair techniques with single and double ring annuloplasties.

For patients with isolated aortic regurgitation, a double sub- and supravalvular annuloplasty has been shown to reduce recurrent aortic regurgitation after aortic valve repair compared with a single subvalvular annuloplasty. The objective of this study was to compare the geometrical and dynamic properties of a single- and double ring annuloplasty in an in vitro model. Eighteen aortic roots from 80 kg pigs were randomized into a control, single ring, and double ring group. Experiments were conducted in a pulsatile in vitro model. Hydrodynamics, radial force measurements at annular and sinotubular level, and 2D echographic imaging were obtained. Both the single- and double ring annuloplasty downsized the aortic annulus and sinotubular junction significantly, and increased the coaptation height. The double ring annuloplasty showed an additional significant increase in coaptation height compared with the single ring (8.5 (0.9) mm to 9.8 (0.8) mm, p < 0.01). The single ring annuloplasty reduced radial forces at both levels, whereas the double ring annuloplasty showed the greatest force reduction of the sinotubular junction. By treating the whole functional aortic annulus, encompassing both the aortic annulus and the sinotubular junction, a greater force reduction is observed. A subvalvular annuloplasty alone is efficient in reducing aortic annulus diameter and increasing coaptation height, however, by treating the sinotubular junction as well, an additional effect is observed on coaptation height, creating a more efficient stabilization. Reduction of annular force-distensibility ratio with the double ring annuloplasty compared with the native controls indicate a sustained stabilizing effect.

Self-rollable Polymer Stent Integrated with Wireless Pressure Sensor for Real-time Monitoring of Cardiovascular Pressure

In this paper, we propose a self-rollable polymer (SU-8) stent integrated with a passive LC pressure sensor for the uninterrupted monitoring of cardiovascular pressure. The design of the LC pressure sensor and polymer stent was optimized by varying the turns of inductor and the stent thickness. A wireless pressure sensor with 30 turns of coils was selected based on the experimental results of inductance and radial force measurements. The sensor was fabricated simultaneously with a stent structure with a thickness of 40 µm on a two-dimensional plane using conventional micromachining processes. The fabricated smart stent was placed inside a silicon tube, and its performance was evaluated as a function of working distance (0–11 mm), working pressure (0–100 mmHg), and different media (air, DI water, and saline). After the preliminary experiment, the entire stent device was encapsulated with a thin parylene C layer, and improvements in biocompatibility were confirmed using a viability test with human umbilical vein endothelial cells. The proposed smart stent is expected be widely used in medical applications owing to its structural excellence.

Steroid eluting biocompatible stent for subglottic stenosis.

Develop a prototype steroid eluting stent suitable for endoscopic treatment of subglottic stenosis. Rectangular-shaped spoke design stents thermally molded into horseshoe-shaped stents were developed using AutoCAD program, and printed on a Lulzbot 3D printer with polycaprolactone (PCL). Kenalog saturated AEROSIL 200 was embedded in the PCL filament. Horizontal radial force measurements were measured at baseline, 1day, and 1month when deformation switched from bending to compression. Amount of Kenalog eluted after 1day, 1week and 1month were measured using HPLC. Horizontal pressure applied to the PCL stent corresponding to a 5-0 ET were 1.27±0.38lb. at baseline, 1.79±0.045lb. at 1day, 1.94±-0.22lb. at 1week and 2.07±0.11lb. at 1month. The horizontal pressure applied to PCL stent corresponding to an 8-0 ET tube were 0.82±0.018lb. at baseline, 1.008±0.045lb. at 1day, 0.95±-0.064lb. at 1week and 1.078±0.021lb. at 1month. The amount of Kenalog eluted increased from 5.78µg/mL at 1day to 15.01µg/mL at 1week to 19.35µg/mL at 1month. This proof-of-concept project is an initial step to demonstrate and create a novel stent in the treatment of subglottic stenosis that applies expansile force on the trachea, elutes steroids and dissolves. Over time the expansile force along the trachea increases allowing the PCL to mucosalize, while it dissolves and continues to elute steroids. The limitations of this in vitro study necessitate experiments on animal models, such as rabbit tracheas to observe for complications and histologic changes. This proof-of-concept project is a Level 5 mechanism-based reasoning study.

In Vitro Evaluation of Mechanical Properties of Segmented Esophageal Self-Expandable Metal Stents: Innovative Test Methods Are Needed.

Background: Self-expanding metal stents (SEMSs) in different geometric shapes are well established treatment options in diseases of the esophagus. Mechanical properties and stent design may have an impact on patient comfort, migration rate, and removability. In this in vitro study, we evaluated mechanical properties of three segmented SEMSs (segSEMSs) for the esophagus with regard to distinct stent sections. Materials and Methods: Radial forces were measured using a testing method distinguishing between circumferential radial and local radial force. The center parts of the segSEMSs were measured for circumferential radial forces without being affected by the flared ends. Axial forces were measured at 20° bending. Results: Circumferential radial force measurements over the full stent length showed substantial differences against measurements of the center parts of the stents as the flared ends falsify test results by up to 53%. Although circumferential radial forces of the center parts were about the same (<10% variances) for all segSEMSs, local radial forces showed considerable differences of up to 26%. One segSEMS showed high axial forces, whereas the other two only needed half of the force (up to 53%) to be bent to 20°. Conclusion: Flared ends of segSEMSs have a substantial impact on radial force measurements and therefore alter test results, confirmed by our separated center part test of segSEMSs. Our innovative setup whereby we compressed the stent in an asymmetric manner (local radial force) and evaluated sections of stents separately, indeed revealed differences to circumferential measurements, leading to a more in-depth knowledge of stent characteristics.

Comparison of the Dacron ring and suture annuloplasty for aortic root repair: an in vitro evaluation.

Increasing evidence shows that annular stabilization is essential in most aortic valve repair procedures. However, a standardized comparison of the 2 commonly used annuloplasty procedures is lacking. We hypothesized that the Dacron ring is more rigid than the polytetrafluoroethylene suture, whereas both procedures decrease annular dimensions. The aim of this study was to compare the biomechanical properties of the ring and suture techniques with native aortic roots in vitro. Eighteen aortic roots explanted from 80-kg pigs were randomized into a Dacron ring group, a suture annuloplasty group and a native control group. Each sample was tested in a pulsatile in vitro model with a force transducer attached to the aortic annulus to obtain radial force measurements, and annular dynamics was evaluated using 2-dimensional echography. Among the 2 annuloplasty procedures, only the Dacron ring group provided a significant reduction in the annular diameter compared with the native group (P < 0.006). Both annuloplasty procedures significantly reduced the geometric orifice area, tenting area and sinus diameter while increasing the coaptation length compared with the native group. Systolic annular distension was retained between groups, although the total radial forces were significantly reduced in the procedure groups compared with the native group (ring 1.07 ± 0.45 N, suture 1.13 ± 0.39 N and native 3.55 ± 1.34 N, P < 0.001). Although both annuloplasty procedures increase coaptation length and decrease geometric orifice area, a significant downsizing of the annulus was achieved using the Dacron ring only. The systolic annular distension was similar to the native aortic root, whereas the radial annular forces were evenly decreased by both annuloplasty procedures. Long-term studies are needed to disclose any difference in long-term effect of the annuloplasty procedures.

Radial stiffness improvement of a flywheel system using multi-surface superconducting levitation

The goal of this research study is the maximization of the levitation force in a flywheel system by the use of more than one permanent magnet with a single ring-shaped HTS material. An analytical model for the radial stiffness of the ring HTS-PM is derived using the frozen image approach. The experimental works are carried out for different polarizations of the permanent magnets, and radial stiffness values are obtained from the radial force measurements. The rotational test of the flywheel system is also realized for different cases. Finally, natural frequencies of the flywheel superconducting magnetic bearing system are experimentally obtained for different combinations of the permanent magnets using a frequency analyzer.

Evaluation of a Bioabsorbable Self-Expandable Vein Stent-Base Made of Poly(L-lactide) In Vitro and In Vivo.

This study was designed to evaluate performance and tissue response to a self-expandable bioabsorbable vein stent-base cut from a tube with enhanced stiffness and strength in vitro and in vivo. A diamond-shaped stent-base was cut from a sequential biaxially strained poly(L-lactide) (PLLA) tube for optimized performance. The performance of the stent-base was evaluated in a finite element analysis model, and validation was attempted in vitro through a cyclic flat-plate compression and radial force measurement. The performance of the stent-base was tested in vivo using 3 sheep with 2 implants each for 2 and 3½ weeks, respectively. In vitro the stent-base showed an elliptical deformation but no fractures. In vivo the stent-base showed adequate radial force and no migration. All implanted stent-bases showed multiple fractures not only at the predicted stress zones but at all connecting points. Fragments of the caudal stent-base stayed in the vein wall indicating sufficient tissue coverage to avoid embolization of the fractured stent pieces, whereas fragments from the cranial device remaining were few. Neointima formation was confirmed histologically at 2 and 3½ weeks. A bioabsorbable self-expandable stent-base made from PLLA for large veins seems feasible, but over time, the PLLA used in this study appears too stiff and lacks the sufficient flexibility to move with the vena cava, causing multiple fractures.

Evaluation of anti-migration properties of biliary covered self-expandable metal stents.

To assess anti-migration potential of six biliary covered self-expandable metal stents (C-SEMSs) by using a newly designed phantom model. In the phantom model, the stent was placed in differently sized holes in a silicone wall and retracted with a retraction robot. Resistance force to migration (RFM) was measured by a force gauge on the stent end. Radial force (RF) was measured with a RF measurement machine. Measured flare structure variables were the outer diameter, height, and taper angle of the flare (ODF, HF, and TAF, respectively). Correlations between RFM and RF or flare variables were analyzed using a linear correlated model. Out of the six stents, five stents were braided, the other was laser-cut. The RF and RFM of each stent were expressed as the average of five replicate measurements. For all six stents, RFM and RF decreased as the hole diameter increased. For all six stents, RFM and RF correlated strongly when the stent had not fully expanded. This correlation was not observed in the five braided stents excluding the laser cut stent. For all six stents, there was a strong correlation between RFM and TAF when the stent fully expanded. For the five braided stents, RFM after full stent expansion correlated strongly with all three stent flare structure variables (ODF, HF, and TAF). The laser-cut C-SEMS had higher RFMs than the braided C-SEMSs regardless of expansion state. RF was an important anti-migration property when the C-SEMS did not fully expand. Once fully expanded, stent flare structure variables plays an important role in anti-migration.

Radial force measurement of endovascular stents: Influence of stent design and diameter.

Angioplasty and endovascular stent placement is used in case to rescue the coverage of main branches to supply blood to brain from aortic arch in thoracic endovascular aortic repair. This study assessed mechanical properties, especially differences in radial force, of different endovascular and thoracic stents. We analyzed the radial force of three stent models (Epic, E-Luminexx and SMART) stents using radial force-tester method in single or overlapping conditions. We also analyzed radial force in three thoracic stents using Mylar film testing method: conformable Gore-TAG, Relay, and Valiant Thoracic Stent Graft. Overlapping SMART stents had greater radial force than overlapping Epic or Luminexx stents (P < 0.01). The radial force of the thoracic stents was greater than that of all three endovascular stents (P < 0.01). Differences in radial force depend on types of stents, site of deployment, and layer characteristics. In clinical settings, an understanding of the mechanical characteristics, including radial force, is important in choosing a stent for each patient.

Unknown pages in the history of vascular stent grafting

Unknown pages in the history of vascular stent grafting

In vitro evaluation of the radial and axial force of self-expanding esophageal stents

Technological innovation in esophageal stent design has progressed over the past decades, but the association between the mechanical properties of stent design and clinical outcome is still poorly understood. In this study the radial force and axial force of currently available stent designs were evaluated using an in vitro testing model. A total of 10 partially and fully covered self-expanding metal stents (SEMSs), a self-expanding plastic stent (SEPS), and an uncovered biodegradable stent were evaluated. Radial force and axial force were measured using a radial force measurement machine (RX500) and a force gauge in an oven at 37°C. A wide range of radial force measurements were observed between the different stent designs, ranging from 4 to 83 N at 15 mm expansion. All braided nitinol stents displayed comparable mechanical characteristics with a relatively low radial force (<150 N) that gradually decreased to 0 N during expansion, whereas plastic and metal stents that were constructed in a nonbraided manner displayed an initially high radial force (>300 N) followed by a steep decline to 0 N during expansion. Conversely, peak axial force was relatively high for braided nitinol SEMSs (>1.5 N), whereas nonbraided SEMSs showed a much lower peak axial force (<1.5 N). Based on radial and axial force data, five groups of stents with comparable mechanical properties could be distinguished. All currently available stents have a characteristic radial and axial force pattern, which may aid in the understanding of the occurrence of specific symptoms and complications after stent placement. Nonetheless, the overall clinical behavior of a stent is probably more complex and cannot be explained by these factors alone.

A Comparative Reliability and Performance Study of Different Stent Designs in Terms of Mechanical Properties: Foreshortening, Recoil, Radial Force, and Flexibility

This study seeks to improve the mechanical performance of stents by conducting reliability performance testing and finite element method (FEM)-based simulations for coronary stents. Three commercially available stent designs and our own new design were tested to measure the factors affecting performance, specifically foreshortening, recoil, radial force, and flexibility. The stents used in the present experiments were 3 mm in working diameter and 18 mm of working length. The results of the experiments indicate that the foreshortening of stents A, B, C, and our new design, D, was equivalent to 2.25, 0.67, 0.46, and 0.41%, respectively. The recoil of stents A, B, C, and D was 6.00, 4.35, 3.50, and 4.36%, respectively. Parallel plate radial force measurements were A, 3.72 ± 0.28 N; B, 3.81 ± 0.32 N; C, 4.35 ± 0.18 N; and D, 4.02 ± 0.24 N. Radial forces determined by applying uniform pressure in the circumferential direction were A, 28.749 ± 0.81 N; B, 32.231 ± 1.80 N; C, 34.522 ± 3.06 N; and D, 42.183 ± 2.84 N. The maximum force of crimped stent at 2.2-mm deflection was 1.01 ± 0.08 N, 0.82 ± 0.08 N, 0.92 ± 0.12 N, and 0.68 ± 0.07 N for each of stents A, B, C and D. The results of this study enabled us to identify several factors to enhance the performance of stents. In comparing these stents, we found that our design, stent D, which was designed by a collaborative team from seven universities, performed better than the commercial stents across all parameter of foreshortening, recoil, radial force, and flexibility.

Radial Force Measurements in Carotid Stents: Influence of Stent Design and Length of the Lesion

Purpose To assess the differences in radial force of carotid stents and whether the length of the lesion influences the measurements. Materials and Methods Different models of tapered stents of similar size (length, 30 mm) were used. The tapered nitinol Acculink, Protégé, and Cristallo Ideale carotid artery stents and the straight, braided Elgiloy carotid Wallstent were compared. A measurement device consisting of three film loops along the stent body connected to aluminium rods with copper strain gauges was developed. Five stents of each type were deployed within 3-mm stenoses in simulated long (26 mm) and short (8 mm) stenoses. Results In the short stenosis simulation, the greatest radial force was seen in the Protégé stent, at 3.14 N ± 0.45, followed by the Cristallo Ideale stent (1.73 N ± 0.51), Acculink (1.16 N ± 0.21), and Wallstent (0.84 N ± 0.10; P < .001). In the long stenosis simulation, peak radial force again was highest in the Protégé stent (1.67 N ± 0.37), but the Acculink stent was second (0.95 N ± 0.12) and the Wallstent third (0.80 N ± 0.06). The Cristallo Ideale stent, in contrast to the short stenosis simulation, produced the least radial force (0.44 N ± 0.13) in the long stenosis simulation ( P = .001). Conclusions Radial forces exerted by carotid stents vary significantly among stent designs. Differences between stent types are dependent on the length of the stenosis. An understanding of radial force is necessary for a well-considered choice of stent type in each individual patient.

Comparison of Carotid Stents: An In-Vitro Experiment Focusing on Stent Design

To examine and compare different carotid stent designs with regard to flexibility, adaptability (adjustability), conformability (compliance) to the vessel, and scaffolding to reduce plaque prolapse and embolization. Six stents of different design were compared (Precise, Acculink, Protégé, Xact, Wallstent, and Cristallo Ideale). Optical microscopy was used to determine exact dimensions and scaffolding of each stent. Radial force was tested using a parallel plate setup, and flexibility (torsion and bending) was measured in water at body temperature. Particle penetration simulation was performed using plastic spheres from 1.5- to 6.0-mm outer diameter. Stent dimensions met the manufacturers' data; none of the products showed any failure during the test program. Cell sizes in the middle part of the stents ranged from 1.36 mm(2) (Wallstent) to 15.10 mm(2) (Acculink). Bending forces at 20 degrees /30 degrees ranged from 0.063 N / 0.074 N (Cristallo Ideale) to 0.890 N / 0.616 N (Xact); forces to achieve torsion at 10 degrees /15 degrees ranged from 0.032 N / 0.043 N (Acculink) to 0.905 N / 1.071 N (Xact). According to the parallel plate method, mean lowest force was measured for Xact (0.765 N), while the Wallstent had the highest force (2.136 N). Mean radial force measurements were lowest for Cristallo Ideale (9.06 N at mid part) and highest for Protégé (24.09 N). The Cristallo Ideale stent at mid part resisted penetration by all but the smallest plastic spheres (1.5-mm spheres penetrated only at 0.65 N); the Precise and Protégé stent had the highest variation in sphere penetration (1.5- to 4.0-mm spheres). Only the Acculink let 6-mm spheres penetrate. Despite comparable stent sizes, these carotid stents showed differences in behavior due to stent design. The open-cell design displayed the greatest flexibility and adaptability to the vessel but easily allowed particle penetration due to the open structure. Closed-cell designs had low flexibility and thus low adaptability to the vessel but high resistance to particle penetration due to the closed-cell design and high scaffolding. The hybrid stent design (Cristallo Ideale) was able to combine both the flexibility of an open-cell structure and the resistance to particle penetration of closed-cell structures.

Measurement of radial and axial forces of biliary self-expandable metallic stents

Efforts to understand the properties of self-expandable metallic stents (SEMSs) through their mechanical properties have progressed. Among them, radial force (RF) is well known as an expanding force, but axial force (AF) has not been measured before. Correlations of these properties to clinical results are not well known. We measured RF and AF of 14 different SEMSs and discussed the results in terms of clinical implications. Experimental study. Measurement of RF and AF of 14 different covered and uncovered SEMSs. RF was measured with an RF measurement machine manufactured by Machine Solution, and AF was measured with in-house equipment. Measurements of RF in the process of expansion showed characteristic patterns closely related to the structures and materials of SEMSs. Results of AF measurement can be classified into 3 groups: high, medium, and low AF, depending on the type of SEMS. AF decreased with an increase of the length of stents. A plot of RF against AF revealed 3 distinguished RF/AF combinations and indicated the importance of understanding the properties by not only RF or AF individually but also by RF/AF combination. In vitro study using measurement equipment. It was demonstrated that a combination of RF and AF is more effective than RF or AF individually in understanding the clinical implications of SEMSs. More work is needed to correlate mechanical properties with clinical results by designing model experiments.

A Plexiglas Research Pump With Calibrated Magnetic Bearings/Load Cells for Radial and Axial Hydraulic Force Measurement

A research pump intended for both flow visualization studies and direct measurement of hydrodynamic radial and axial forces has been developed. The impeller and the volute casing are constructed from Plexiglas which facilitates optical access for laser velocimetry measurements of the flow field both inside the impeller and in the volute casing. The pump housing is designed for flexibility allowing for each interchange of impellers and volute configurations. The pump rotor is supported by three radial magnetic bearings and one double acting magnetic thrust bearing. The magnetic bearings have been calibrated to characterize the force versus coil current and air gap relationship for each bearing type. Linear calibration functions valid for rotor eccentricities of up to 2/3 of the nominal bearing clearances and force level of ±58 N (13 lbf) and ±267 N (60 lbf) for the radial and axial bearings, respectively, were found. A detailed uncertainty analysis of the force calibration functions was conducted such that meaningful uncertainty bounds can be applied to in situ force measurements. Hysteresis and eddy current effects were quantified for each bearing such that their effect on the in situ force measurements could be assessed. By directly measuring the bearing reaction forces it is possible to determine the radial and axial hydraulic loads acting on the pump impeller. To demonstrate the capability of the magnetic bearings as active load cells representative hydraulic force measurements for a centered 4 vane 16 degree log spiral radial flow impeller operating in a single tongue spiral volute casing were made. At shut-off a nondimensional radial thrust of 0.084 was measured. A minimum nondimensional radial thrust of about 0.007 was observed at the nominal design flow. The nondimensional radial thrust increased to about 0.019 at 120 percent of design flow. The nondimensional axial thrust had a maximum at shut-off of 0.265 and decreased steadily to approximately 0.185 at 120 percent of design flow. Two regions of increasing axial thrust, in the flow range 75 to 100 percent of design flow, were observed. The measurements are compared to radial and axial force predictions using classical force models. The direct radial force measurements are compared to a representative set of radial force measurements from the literature. In addition, the directly measured radial force at design flow is compared to a single representative radial force measurement (obtained from the literature) calculated from the combination of static pressure and net momentum flux distribution at the impeller exit.

Development of new drill geometry and its performance evaluation

A new type of drill, namely, the crankshaft multifacet drill, has been developed for crankshaft drilling. Thrust has been selected as a main index for the development of this drill geometry. The crankshaft multifacet drill can reduce the thrust by 25.2% under operating conditions identical to those of the conventional split point drill. This indicates that drill life could be increased. Under accelerated life test conditions, this new drill is capable of producing at least 25% more oilholes than would be produced by the conventional split point drill. Test results for radial force measurements, chip breaking capability, exit burr evaluation, and drill wear comparison have also been evaluated. This drill yields much better performance in all aspects than the drill currently used in industry. The crankshaft multifacet drill can not only enhance productivity but also improve hole quality as compared to the conventional split point drill.

Instrumentation and calibration of a single-punch press for measuring the radial force during tableting

A single-punch tablet press was instrumented for radial force measurement during tableting by cutting out segments from the die, leaving 5.0 mm of die wall, and by applying strain gauges to these thinner parts. Active horizontal gauges were connected to temperature-compensating vertical gauges to Torm a Wheatstone bridge with two fixed resistors in the bridge amplifiers. The instrumentation was dynamically calibrated at tableting speed (30 rpm) with rubber-like materials lubricated with molybdenum disulphide (Molykote). The die wall signals were reproducible and increased linearly with the applied pressure. The signals increased with increasing height of the compact. The position of the lower punch had a marked influence on the response. When the lower punch was in a position 10.2 mm below the upper surface of the die, the signal at constant pressure was proportional to the cross-sectional area of the compact. At this position the die wall pressure could be calculated from the regression line of signal/cross-sectional area vs applied pressure. This regression was the same for all tested rubber materials and the estimated relative standard deviation of single determinations at 100 MPa was about 3%.